A photovoltaic power generating system generally includes photovoltaic panels, an inverter, a transformer, and other apparatuses. A positive electrode and a negative electrode of a photovoltaic panel are connected to two input ends of the inverter. The inverter has three output ends connected to the transformer, and outputs a three-phase alternating current. Generally, the photovoltaic panels are classified into a P-type photovoltaic panel and an N-type photovoltaic panel. When a voltage between a negative electrode of the P-type photovoltaic panel and ground is negative, or when a voltage between a positive electrode of the N-type photovoltaic panel and ground is positive, output power degradation of the photovoltaic panel is caused. This is referred to as a PID potential induced degradation, potential induced degradation (PID) effect of the photovoltaic panel.
To suppress the PID effect of the photovoltaic panel, a circuit shown in FIG. 1 is used in the prior art. A direct current voltage source is connected between a negative electrode of a P-type photovoltaic panel string and the ground, to increase a negative voltage between the negative electrode of the P-type photovoltaic panel string and the ground, or a direct voltage source is connected between a positive electrode of an N-type photovoltaic panel string and the ground, to lower a positive voltage between the positive electrode of the N-type photovoltaic panel string and the ground, so as to suppress the PID effect of the photovoltaic panel string.
When the voltage between the positive electrode or the negative electrode of the photovoltaic panel and the ground is controlled by using the method, the positive electrode or the negative electrode of each photovoltaic panel needs to be connected to a direct voltage source by using a lead, leading to an increase in lead costs and relatively complex wiring.